As I thought about it, it seems the fewer the syllables, the less risky the name. So Aragorn and Galadriel seem like they'd have more people looking at you with a puzzled expression than Beren and Arwen. But other short names sound odd in English no matter what: I'd avoid Frodo for that reason.

The longer the name also means it's more likely to be shortened to a nickname, so Aragorn might become Gorn, and Galadriel become Gala or Riel. I wouldn't want my kid called Gorn; it sounds unpleasant somehow, like an expletive. "Gorn! I hurt my foot."

As for reverse nicknames, I work with a man named Sam and sometimes call him Samwise. I'm not sure if he gets the reference or not, but he doesn't mind that I do, since it sounds flattering on its own.